Determining the network topology of a communication network

ABSTRACT

A network management agent, device or module determine the network topology of a communication network based on at least one neighbor network or end device identity and corresponding network link communication delay collected from, determined by, and stored in a Management Information Base of, at least one first network device of the communication network. Neighbor identities and communication delays are determined according to the IEEE 1588 standard.

RELATED APPLICATIONS

This application claims priority as a continuation application under 35U.S.C. §120 to PCT/EP2013/063003, which was filed as an InternationalApplication on Jun. 21, 2013 designating the U.S., and which claimspriority to European Application 12172854.7 filed in Europe on Jun. 21,2012. The entire contents of these applications are hereby incorporatedby reference in their entireties.

FIELD

The present disclosure relates to determining the topology of acommunication network of an industrial process control system, such as asubstation automation system.

BACKGROUND INFORMATION

In order to discover and determine the topology of a communicationnetwork, it may be required that network devices report knowledge oftheir local topology to a network management device. Several productsexist on the market, such as, for example, Hirschmann's HiVision,wherein protocols like ARP (ARP: Address Resolution Protocol), ICMP(ICMP: Internet Control Message Protocol), or SNMP (SNMP: Simple NetworkManagement Protocol) are used. These tools operate on layer 3, forexample, using IP addresses (IP: Internet Protocol) of the networkdevices, and are not directly aware of layer 2 devices orconfigurations, such as, for example, media converters, repeaters,unmanaged bridges or switches operating on layer 2 only.

On the link layer, namely on layer 2, the topology of communicationnetworks may be discovered using the vendor-neutral Link Layer DiscoveryProtocol (LLDP, IEEE 802.1AB) or using vendor-specific protocols such asMicrosoft's Link Layer Topology Discovery (LLTD), the Cisco DiscoveryProtocol, or any other vendor-specific protocol. In the LLDP, networkdevices send through each of their network interfaces, at a fixedinterval, a so-called Link Layer Discovery Protocol Data Unit (LLDPDU)in the form of an Ethernet frame, which has its destination MAC address(MAC: Media Access Control) set to a specific multicast address.Information gathered with LLDP is stored in the network devices in amanagement information database (MIB) and may include system names, portnames, VLAN names, etc. The MIB of the network devices may be queriedwith the SNMP in order to discover the network nodes and establish thetopology of a network in which all devices are LLDP-enabled. The latterprerequisite, however, is not fulfilled in most automation networksdeployed today.

SUMMARY

An exemplary embodiment of the present disclosure provides a method fordetermining the network topology of a communication network including atleast one first network device connected through at least one networklink to at least one neighboring network device. The at least one firstnetwork device and the at least one neighboring network device aresynchronized according to the IEEE 1588 standard. The exemplary methodincludes determining, by each of the at least one first network device,an identity of the at least one neighboring network device and acommunication delay of the at least one network link, respectively. Theexemplary method also includes collecting, by a network manager, therespective determined identity and communication delay, and determininga network topology of the communication network including a length ofthe at least one network link therefrom.

An exemplary embodiment of the present disclosure provides a networkmanagement agent for determining the network topology of a communicationnetwork including at least one first network device. Each first networkdevice is connected through at least one network link to at least oneneighboring network device. The at least one first network device andthe at least one neighboring network device are synchronized accordingto the IEEE 1588 standard. The network management agent includes aprocessor configured to, by executing a computer program tangiblyrecorded on a non-transitory computer-readable recording medium of thenetwork management agent, collect, from each of the at least one firstnetwork device, an identity of the at least one neighboring networkdevice and a communication delay of the at least one network link,respectively, and determine the network topology of the communicationnetwork including a length of the at least one network link therefrom.

An exemplary embodiment of the present disclosure provides anon-transitory computer-readable recording medium having a computerprogram tangibly recorded thereon that, when executed by a processor ofa computer processing device, causes the processor to carry out a methodfor determining the network topology of a communication networkincluding at least one first network device connected through at leastone network link to at least one neighboring network device. The atleast one first network device and the at least one neighboring networkdevice are synchronized according to the IEEE 1588 standard. Theexemplary method includes determining, by each of the at least one firstnetwork device, an identity of the at least one neighboring networkdevice and a communication delay of the at least one network link,respectively. The exemplary method also includes collecting, by anetwork manager, the respective determined identity and communicationdelay, and determining a network topology of the communication networkincluding a length of the at least one network link therefrom.

BRIEF DESCRIPTION OF THE DRAWINGS

Additional refinements, advantages and features of the presentdisclosure are described in more detail below with reference toexemplary embodiments illustrated in the drawings, in which:

FIG. 1 shows a sample network topology of a communication networkaccording to an exemplary embodiment of the present disclosure, and

FIG. 2 shows an exemplary sequence of steps for determining the networktopology of a communication network.

DETAILED DESCRIPTION

Exemplary embodiments of the present disclosure provide a method and anetwork management agent for determining the topology of a communicationnetwork which is widely deployable and which includes additional aspectsrelating to the network topology. According to an exemplary embodiment,the communication network includes one or more first network devices,which are each connected through one or more network links to one ormore neighboring network devices. The one or more first network devicesand the one or more neighboring network devices are synchronizedaccording to the IEEE 1588 standard entitled “Precision Time Protocol.”Exemplary embodiments of the present disclosure avoid at least some ofthe disadvantages of the prior art in communication network topologydetermination.

According to an exemplary embodiment of the present disclosure, thenetwork topology of a communication network is determined, where thecommunication network includes one or more first network devices eachconnected through one or more network links to one or more neighboringnetwork devices or peer devices includes the following steps. Each ofthe one or more first network devices determines an identity of each ofthe respective neighboring network devices as well as a communicationdelay, or peer delay, between the first network device and each of therespective neighboring network devices according to the above-describedIEEE 1588 standard. The determined identities of the respectiveneighboring network devices and the communication delays of therespective communication links are collected by a network manager, andexploited to determine the network topology of the communication networkincluding a length of the one or more network links.

According to an exemplary embodiment the present disclosure, from thecommunication delays, additional conclusions can be drawn regarding somephysical, as opposed to purely logical, aspects of the network topology.For example, the inter-device communication delays of a deployed networkmay be converted into distances or cable lengths and compared to thecorresponding intended or design parameters. Furthermore, excessivecommunication delays may be interpreted as being due to unwanted devicesin the communication network that do not adhere to the path delaydetermination protocol.

Exemplary embodiments of the present disclosure take advantage of thefact that in communication networks synchronized according to the IEEE1588 standard, the network devices synchronize to a reference clock uponreceipt of a synchronization message. In such networks, as the portthrough which a synchronization message arrives can vary uponreconfiguration of the network or change of the master clock, eachdevice regularly calculates the peer delays on all of its ports. Byidentifying the neighboring devices and determining the communicationdelays to neighboring network devices, a communication device determinesits local network topology. A network manager ultimately collects theselocal network topologies and determines the network topology of thecommunication network by reverting to known protocols such as SNMP.Moreover, an additional parameter describing the network topology isprovided because the communication delay between the network devices isdetermined. This allows for a check to be made if the networkcorresponds to the engineering drawings and can determine if thephysical distance has been respected and if unauthorized devices havebeen inserted.

In accordance with an exemplary embodiment, the one or more firstnetwork devices transmit a peer delay request message to the one or moreneighboring network devices. The peer delay request message is receivedby the one or more neighboring network devices and triggers theneighboring network devices to transmit a peer delay response message tothe one or more first network devices. The peer delay response messageis received by the one or more first network devices and enables thelatter to determine the one or more communication delays between the oneor more first network devices and the one or more neighboring networkdevices as provided for in IEEE 1588. In other words, the networkdevices send spontaneously to all devices to which they are connected apeer delay request message to which the peer responds with a peer delayresponse message containing its identity and a time stamp indicating thetime difference between the instant the device received the peer delayrequest and responded with the peer delay response message and possiblythe absolute time as seen on the local clock of the peer, as well. Thus,the sender of the peer delay request can determine the identity of andthe line propagation delay to all its peers and thus generate networktopology information. The IEEE 1588 standard is becoming a widelyavailable standard in network devices, and the only addition required isthe ability to report the identity of the peer and the value of the peerdelay to network management.

In accordance with an exemplary embodiment, a broadcast device isconfigured to broadcast a synchronization message to the one or morefirst network devices enabling the one or more first network devices toreceive the synchronization message via a first port or networkinterface, and triggering the one or more first network devices totransmit the synchronization message via one or more second ports ornetwork interfaces to neighboring nodes. Accordingly, thesynchronization message is broadcasted to network devices not directlyconnected to the broadcast device. The synchronization message may thenbe exploited in determining the communication delays, for example, inconnection with response messages transmitted by the neighboring nodesto the one or more first network devices.

In accordance with an exemplary embodiment, a graphical network diagramis generated showing the actual network topology of the communicationnetwork. The actual network topology of the communication network canthus be easily verified.

In accordance with an exemplary embodiment, a graphical network diagramshowing the design of the network topology of the communication networkis updated. For example, updating the graphical network diagram mayinclude marking missing or erroneous network links. Accordingly, theactual network topology of the communication network including idlelinks can thus be easily compared to a designed network topologyaccording to design requirements.

In accordance with an exemplary embodiment, a network management agentis configured to collect through, for example, SNMP (SNMP: SimpleNetwork Management Protocol) from a MIB (MIB: Management InformationBase) stored in the one or more first network device, the one or morecommunication delay together with the MAC address (MAC: Media AccessControl) of the one or more first network device. By collecting the MACaddress, the interfaces of the network devices are uniquely identified.Moreover, the communication delay of the network links provideadditional information about the network topology of the communicationnetwork. As data is stored in widely deployed MIB and collected to thewidely available SNMP, collection of the data is widely deployable invarious communication networks.

Exemplary embodiments of the present disclosure relate to a networkmanagement agent, device, or module for determining the network topologyof a communication network based on at least one neighbor network or enddevice identity and corresponding network link communication delaycollected from, determined by, and stored in a Management InformationBase of, at least one first network device of the communication network.Neighbor identities and communication delays are preferably determinedby reverting to the IEEE 1588 standard entitled “Precision TimeProtocol.”

Exemplary embodiments of the present disclosure are describedhereinafter in terms of the functions performed by the networkmanagement agent, device or module, which may be collectively referredto as devices of the present disclosure. It is to be understood that thefunctions of these devices as described hereinafter are eachrespectively implemented in one or more computer processing devicesconfigured to individually and/or collectively perform the functions ofthe network management agents, devices or modules. Such computerprocessing devices may be a personal computer or server computer eachappropriately programmed to carry out the respective functions of thedevices as described herein. The computer processing devices eachinclude a processor and a non-transitory computer-readable recordingmedium, which is a non-volatile memory such as a ROM, hard disk drive,flash memory, optical memory, etc. The non-transitory computer-readablerecording medium has tangibly recorded thereon a computer program and/orcomputer-readable instructions which, when executed by the processor ofthe computer processing device, causes the processor to perform theoperative functions of the devices as described herein. The processormay be a general-purpose processor such as those produced by Intel® orAMD®, for example. Alternatively, the processor may be an applicationspecific processor which is specifically designed for the computer(s) ofthe respective device(s).

FIG. 1 shows a sample network topology of a communication network 1including several network devices 10, 20, 30, 40, 50 and network enddevices 21, 41, 42, 51, 52. In particular, the communication network 1may be an Ethernet based communication network, wherein data packets aretransported by network devices 10, 20, 30, 40, 50, such as, for example,bridges, routers, servers, computers, etc., which are connected throughnetwork links 11, 12, 13, 14, 15, 16. The network links may include inparticular Ethernet network cables or fiber optical cables. Thecommunication network 1 may be designed to be used in an industrialautomation system.

The network devices 10, 20, 30, 40, 50 are designed to receive andforward network traffic, and they may themselves consume parts of thereceived traffic. For example, a bridge according to the IEEE 802.1Dstandard is designed to receive and transmit network traffic on a layer2, i.e. link layer, of the communication network 1. As bridges operateon layer 2 only, they are not discoverable on layer 3, such that, forexample, an application running on a server at layer 3 is not able todiscover the layer 2 topology of the communication network 1. However,layer 2 topology is required in order to verify that the communicationnetwork 1 has been properly installed and configured, for example, orthat the communication network 1 is operating without errors orfailures.

As shown in FIG. 1, the communication network 1 includes a broadcastdevice 21, which may include a grandmaster with a grandmaster clock MCaccording to the IEEE 1588 standard or a similar protocol, such as, forexample, IEEE 802.1AS. As indicated in FIG. 1, the broadcast device 21may be connected to a GPS receiver (GPS: Global Positioning System),such that the grandmaster clock MC may be synchronized with an accuratetime from one or more GPS satellites, for example. However, thegrandmaster clock MC may receive a precise time through any othersuitable device, in particular with a high-stability oscillator.

The broadcast device 21 broadcasts a synchronization message 2, which isreceived by network devices 10, 20, 30, 40, 50 of the communicationnetwork 1 and all end devices 41, 42, 51, 52. The network devices 10,20, 30, 40, 50 and the end devices are configured according to the IEEE1588 standard, for example. Accordingly, the network devices 10, 20, 30,40, 50 may include a transparent clock TC and may be configured toforward the synchronization message 2 received on one of its networkinterfaces to all its other network interfaces. According to the IEEE1588 standard, for example, a correction is computed which is sent inthe same synchronization message 2′ or in a subsequent synchronizationmessage 2″ (one-step or two-step synchronization). Hence, thesynchronization message 2 is broadcasted from the grandmaster device 21including the master clock MC to the network devices 10, 20, 30, 40, 50,which comprise transparent clocks TC, of the communication network 1.

To compute the time correction due to the link delay, all networkdevices of the communication network 1 may be configured to transmit oneor more peer delay request messages 3 through all their networkinterfaces, which are received by one or more peer neighboring devices,for instance device 10 sends such peer delay request to network devices20, 30, 40 and to the end device 21. The device receiving the peer delayrequest message 3 can be configured to answer immediately with a peerdelay response message 4 back to the originator of the peer delayrequest, in this case the network device 10.

The network devices 10 computes the communication delays d12, d13, d14to its neighbors by time-stamping the peer delay request message 3 andreceiving the peer delay response message 4 which also contains thesending time. For example, the peer delay request message 3 may includea first timestamp indicating the time when the peer delay requestmessage 3 was sent. The peer delay response message 4 may furtherinclude a second timestamp indicating the time difference between thereception of message 3 and the sending of message 4, which is called thelatency. The originator records the time at which the peer responsemessage 4 was returned. Hence, the communication delays d12, d13, d14may be computed by subtraction of the first timestamp from the secondtimestamp and subtracting the received latency. The computation ofcommunication delays may also be performed by the end devices 41, 42,51, 52, which comprise ordinary clocks OC, and by the broadcast device21, which includes the master clock MC.

The communication delays d12, d13, d14 between the network devices 10,20, 30, 40, 50 are a function of the cable length. Accordingly, on thebasis of the computed communication delays d12, d13, d14, the cablelength between network devices 10, 20, 30, 40, 50 may be computed.Moreover, network devices which do not conform to, for example, the IEEE1588 standard may be detected, as such network devices introduce asignificant additional communication delay, which is well in excess ofany expected cable propagation delays. The wave propagation speed s on anetwork cable may range from .59c to .77c (c: speed of light).Accordingly, the delay on a network cable segment of the length of 1 mayrange from 4.3 ns to 5.6 ns. On the other hand, the switching delay ofnetwork devices such as network switches or bridges may be in the rangeof 10-40 μs, or even higher, such that the presence of such devices thatare not equipped with IEEE 1588 TCs can be easily detected. Bridgingdevices not equipped for the IEEE 1588 do not respond at all and areeasily detected by a timeout.

Messages between the network devices 10, 20, 30, 40, 50 may be sentusing multicast messaging or unicast transmission. The messages mayconform to the IEEE 1588 standard, or any other similar standard. Incase the messages are transmitted on layer 3, the messages may betransmitted using IP packets. For example, UDP packets may betransmitted (UDP: User Datagram Protocol). Messages may also betransmitted on layer 2 through encapsulation in IEEE 802.3 Ethernet, orany other layer 2 protocol.

The determined communication delays d12, d13, d14 between the networkdevices 10, 20, 30, 40, 50 may be stored in a management informationbase (MIB) or in any other database. The MIB may be stored on thenetwork devices 10, 20, 30, 40, 50 or one of the end devices 21, 41, 42,51, 52. Hence, each network device 10, 20, 30, 40, 50 may have storedthereon the local topology to its neighboring devices. For example,network device 10 according to FIG. 1 may have stored the delay d12through network link 12 to the network device with numeral 20, the delayd14 through network link 14 to the network device with numeral 40, thedelay d13 through network link 13 to the network device with numeral 30,and the delay d1M through network link 1M to the grandmaster device 21.

The data stored in the MIB of the network device with label 10, forexample, may include the MAC address (MAC: Media Access Control) of thenetwork device with label 10 and the MAC address of the neighboringnetwork devices 20, 30, 40 together with the determined communicationdelays d12, d13, d14 to the neighboring network devices. As such, theMIB includes the local network topology of the network device with label10, namely the information about network links 12, 13, 14 andneighboring network devices 20, 30, 40 as well as the information abouta distance or communication delay between the network device with label10 and the neighboring network devices 20, 30, 40.

A network management agent A may be configured to collect the MIB or anyother database stored in the network devices 10, 20, 30, 40, 50. Forexample, data of the MIB of the network devices 10, 20, 30, 40, 50 maybe collected through the SNMP protocol (SNMP: Simple Network ManagementProtocol). Collection of the MIB or the database stored in the networkdevices 10, 20, 30, 40, 50 may be performed through any other protocol,such as, for example, IEC 61850, which is a widely-used standard forelectrical substation automation systems.

Accordingly, the network management agent A may collect the informationabout network links 12, 13, 14 between network devices 10, 20, 30, 40,50 as well as the distance or communication delay d12, d13, d14.

The network management agent A may be configured to generate a graphicalnetwork diagram showing the actual topology of the communicationnetwork. The network diagram does not necessarily reflect thegeographical location of the network devices. However, the distances orcommunication delays between the network devices may well be showngraphically.

The network management agent A may be configured to update a graphicalnetwork diagram showing the design of the network topology of thecommunication network. Hence, when engineering a communication network,the network configuration may be designed according to designrequirements, which may include geographical allocation of the networkdevices 10, 20, 30, 40, 50, e.g. ordered by bays, cabinets, etc.,wherein data may be coded in a wiring diagram or in an SCD fileaccording to the IEC 61850 standard. Knowing the physical dimensions, anengineering tool, which is an example of the above-described computerprocessing device, can predict the approximate values of the linkdelays. The communication network may be commissioned according to thedesign requirements. In a graphical network diagram of the commissionedcommunication network, those network links are graphically indicatedwhich have been wrongly commissioned, which are erroneous/missing orwhich show a communication delay exceeding a certain value. This helpsdetect devices which are not working properly, devices of the wrong typeor unwanted devices that could ruin the synchronization.

FIG. 2 shows schematically exemplary steps for the determination of thenetwork topology of a communication network 1 according to an exemplaryembodiment of the present disclosure. In step S1, a synchronizationmessage is broadcasted. In step S2, the synchronization message 2 isreceived by the one or more first network devices 10 on one of itsnetwork interfaces. In step S3, the communication delays d12, d13, d14between the one or more first network devices 10 and the one or moreneighboring network devices 20, 30, 40 is determined. In step S4, thedetermined one or more communication delays d12, d13, d14 are collected,for example, through SNMP from a MIB stored in the one or more firstnetwork devices 10. In step S5, the one or more communication delaysd12, d13, d14 are used to determine the network topology of thecommunication network 1.

In step S21, the synchronization message 2 triggers transmission of apeer delay request message 3 to the one or more neighboring networkdevices 20, 30, 40. In step S22, the peer delay request message 3triggers transmission of a peer delay response message 4 to the one ormore first network devices 10. In step S3, the peer delay responsemessage 4 enables determination or computation of the one or morecommunication delays d12, d13, d14 between the one or more first networkdevices 10 and the one or more neighboring network devices 20, 30, 40.

In step S20, the synchronization message 2 is received on one of thenetwork interfaces of the one or more first network devices 10 and thesynchronization message is transmitted to one or more of the othernetwork interfaces.

In step S51, a graphical network diagram showing the actual networktopology of the communication network is generated. In step S52, agraphical network diagram showing the design of the network topology ofthe communication network is updated.

It will be appreciated by those skilled in the art that the presentinvention can be embodied in other specific forms without departing fromthe spirit or essential characteristics thereof. The presently disclosedembodiments are therefore considered in all respects to be illustrativeand not restricted. The scope of the invention is indicated by theappended claims rather than the foregoing description and all changesthat come within the meaning and range and equivalence thereof areintended to be embraced therein.

What is claimed is:
 1. A method for determining the network topology of a communication network including at least one first network device connected through at least one network link to at least one neighboring network device, the at least one first network device and the at least one neighboring network device being synchronized according to the IEEE 1588 standard, the method comprising: determining, by each of the at least one first network device, an identity of the at least one neighboring network device and a communication delay of the at least one network link, respectively; and collecting, by a network manager, the respective determined identity and communication delay, and determining a network topology of the communication network including a length of the at least one network link therefrom.
 2. The method according to claim 1, comprising: transmitting, by the at least one first network device, a peer delay request message to the at least one neighboring network device; transmitting, by the at least one neighboring network device, a peer delay response message to the at least one first network devices; and determining, by the at least one first network device, the at least one communication delay between the at least one first network device and the at least one neighboring network device from the peer delay request message and the peer delay response message.
 3. The method according to claim 1, comprising: receiving a broadcast synchronization message on a first network interface of the at least one first network device; transmitting, by the at least one first network device, the synchronization message on at least one second network interface to the at least one neighboring network device; transmitting, by the at least one neighboring network device, a response message to the at least one first network device; and determining, by the at least one first network device, the at least one communication delay between the at least one first network device and the at least one neighboring network devices from the synchronization message and the response message.
 4. The method according to claim 1, comprising: generating a graphical network diagram showing an actual network topology of the communication network.
 5. The method according to claim 1, comprising: updating a graphical network diagram showing the design of the network topology of the communication network.
 6. The method according to claim 1, comprising: collecting the at least one communication delay through SNMP (SNMP: Simple Network Management Protocol) from a MIB (MIB: Management Information Base) stored in the at least one first network devices, together with a MAC address (MAC: Media Access Control) of the at least one first network device and the MAC address of the corresponding at least one neighboring network device.
 7. The method according to claim 2, comprising: generating a graphical network diagram showing an actual network topology of the communication network.
 8. The method according to claim 2, comprising: updating a graphical network diagram showing the design of the network topology of the communication network.
 9. The method according to claim 2, comprising: collecting the at least one communication delay through SNMP (SNMP: Simple Network Management Protocol) from a MIB (MIB: Management Information Base) stored in the at least one first network devices, together with a MAC address (MAC: Media Access Control) of the at least one first network device and the MAC address of the corresponding at least one neighboring network device.
 10. The method according to claim 3, comprising: generating a graphical network diagram showing an actual network topology of the communication network.
 11. The method according to claim 3, comprising: updating a graphical network diagram showing the design of the network topology of the communication network.
 12. The method according to claim 3, comprising: collecting the at least one communication delay through SNMP (SNMP: Simple Network Management Protocol) from a MIB (MIB: Management Information Base) stored in the at least one first network devices, together with a MAC address (MAC: Media Access Control) of the at least one first network device and the MAC address of the corresponding at least one neighboring network device.
 13. The method according to claim 4, comprising: updating a graphical network diagram showing the design of the network topology of the communication network.
 14. The method according to claim 13, comprising: collecting the at least one communication delay through SNMP (SNMP: Simple Network Management Protocol) from a MIB (MIB: Management Information Base) stored in the at least one first network devices, together with a MAC address (MAC: Media Access Control) of the at least one first network device and the MAC address of the corresponding at least one neighboring network device.
 15. A network management agent for determining the network topology of a communication network including at least one first network device, each first network device being connected through at least one network link to at least one neighboring network device, the at least one first network device and the at least one neighboring network device being synchronized according to the IEEE 1588 standard, the network management agent having a processor configured to, by executing a computer program tangibly recorded on a non-transitory computer-readable recording medium of the network management agent: collect, from each of the at least one first network device, an identity of the at least one neighboring network device and a communication delay of the at least one network link, respectively; and determine the network topology of the communication network including a length of the at least one network link therefrom.
 16. A non-transitory computer-readable recording medium having a computer program tangibly recorded thereon that, when executed by a processor of a computer processing device, cause the processor to carry out a method for determining the network topology of a communication network including at least one first network device connected through at least one network link to at least one neighboring network device, the at least one first network device and the at least one neighboring network device being synchronized according to the IEEE 1588 standard, the method comprising: determining, by each of the at least one first network device, an identity of the at least one neighboring network device and a communication delay of the at least one network link, respectively; and collecting, by a network manager, the respective determined identity and communication delay, and determining a network topology of the communication network including a length of the at least one network link therefrom. 